1. Technical Field
The invention refers to a procedure for reducing interference in the transmission of an electrical communication signal which preferably is a voice signal but which could also be a data signal. In the transmission of voice signals over faulty channels, the voice signals are generally superimposed with additional interference. This interference can have different causes, for example crosstalk on lines, interference from power transmission lines, bit errors or burst errors in the case of digital transmission routes or echoes on the lines. The faulty signals caused by this interference can take on such great amplitudes that the audibility of the voice on the received voice signal is decreased significantly.
2. Discussion of Related Art
To reduce the faulty parts of a voice signal which has been received with interference, it is generally well known that band-stop filters can be used which suppress the interference in a particular frequency range. In this, the disadvantage is that parts of the frequency of the voice signal are also suppressed.
If the faulty signal can be established over a great amplitude which exceeds a certain threshold, for example in the HF or ZF demodulator range of the receiver, then the output signal can be switched to silent. Such a procedure is used, for example, in UKW radio receivers and amateur devices.
In addition, it is known in the case of a statistically steady-state noise how to estimate and buffer the noise in the voice breaks and to subtract the noise spectrum from this noise during speech, as in W. Reich: Adaptive systems for the reduction of environmental noise in voice transmissions, Dissertation at the Institute for Communication Technology, the University of Karlsruhe, 1985. In the described procedure, the time function of the voice is transformed by means of a Fast-Fourier transformation into a frequency spectrum; the frequency spectrum is analyzed with regard to unwanted noise and transformed back for further processing in the time range. Due to the multiple Fast-Fourier transformation, this procedure demands great computer input. In addition, disturbance within the voice spectrum cannot be recognized.